1. Field of the Invention
The present invention relates to a light source unit for use in a display device such as a projector, and a display device using such light source unit.
2. Description of the Related Art
Rays of light emitted from a light emitting element of a lamp valve of a light source unit for use in a display device such as a projector are focused on an incident plane of a glass or plastic rod (or light tunnel of a hollow cylinder with an internal reflective surface) by a reflector having a light reflecting function on a front or back surface thereof.
Often used as one of the shapes of the reflective surfaces of the reflectors is a concave surface coinciding with an outer surface of one of two halves into which a spheroid is bisected along its plane perpendicular to its axis coinciding with an optical axis. In this case, it is intended that the reflector is disposed such that first and second focuses of the spheroid align on the optical axis, and the light emitting element of the lamp and the center of the incident plane of the rod are disposed at the first and second foccal points, respectively, of the spheroid to securely focus the rays of light emitted by the light emitting element onto an end of the rod to thereby cause the rays of light to enter the rod.
A cross-sectional shape of the lamp valve obtained when the lamp valve is cut along a plane containing the optical axis does not provide a concentric shape whose center coincides with the light emitting element of the lamp.
Therefore, rays of light emitted from the light emitting element are refracted when they pass through the lamp valve (for example, the lamp valve having enclosed the light emitting element therein acts as a convex lens to thereby refract the rays of light).
Even when the respective rays of light emitted from the outer surface of the lamp valve are extended toward the light emitting element, a virtual image of the light emitting element deviates generally from the optical axis.
Therefore, the respective rays of light emitted from the light emitting element of the lamp disposed at the position in the reflector coinciding with-the first focal point, passing through the lamp valve and refracted by the refractor are not completely focused on the position coinciding with the second focal point. Thus, the problem with the light source unit is that part of the rays of light from the lamp does not enter the rod and the percentage of using the rays of light from the lamp is low.